The Mighty Microcontroller

By Miles Budimir, Senior Editor

As prices drop and the available number of functions increase, new microcontroller offerings are ready to add smarts to your latest design.

Microcontrollers are microprocessor’s strong little cousin. Designed to handle specific control tasks, they are generally easier to program, cost less and require much less engineering support.

The first microcontrollers were introduced to the market in the early 1970s, from both Texas Instruments (TI) and Intel. A microcontroller is essentially a self-contained control system with a processor, memory and peripherals. They are used most often in so-called embedded systems, which are computing systems with a specific function literally embedded within a larger electrical or mechanical system.

As microcontroller prices continue to drop, they are being used in newer applications where cost would have been a barrier in earlier times. Also, new families of microcontrollers are getting physically smaller in size, making them suitable for applications where physical space was a chief constraint. For instance, some consumer reward cards now have tiny microcontrollers embedded in them, which enables a whole new range of features and functions that weren’t possible before, for very little cost and design effort. Another factor playing a role in microcontroller popularity is the focus on energy efficiency in electric motors. A simple microcontroller system can help improve energy efficiency and that’s another reason why they’re becoming more attractive to designers.

Mixed-Signal Microcontrollers
Some of the best examples of what’s new with microcontrollers come from Microchip Technology, a microcontroller manufacturer in Arizona. For well over two decades, the company has provided microcontrollers for industrial and commercial grade applications where cost and reliability are prime factors.

The standard microcontrollers available today are really complete systems on a chip. Case in point: the latest offering from Microchip. Its PIC24F GC family contains a full range of functions on a single chip including 16-bit and 12-bit A-to-D converters, D-to-A converters, dual op-amps, comparators, and voltage references, in addition to port communications (UART, SPI, PWM, timers, USB) as well as the standard controller functions, in this case a 16 MIPS 32 MHz core and memory including Flash, RAM and a 6-channel DMA.

That’s a lot of horsepower in one package. Hence, this makes designing a system with microcontrollers that much easier, simpler and cost effective. Example applications are plentiful, including medical applications such as blood pressure meters, glucose monitors and wearable sensors.

A vivid example from this new series illustrates how designs are simplified with the new microcontroller family. With older microcontrollers, PC board space would need to include space for ADCs, USB controller chips, DACs, and other peripheral components. What the new family does is integrate all of these functions onto the chip, saving PC board area and cost, enabling smaller designs and simplifying the design procedure. In this way the bulk of design work is moved away from the hardware side of things (board layout, interconnect, etc.) to the software side.

Microchip’s PIC 24F GC family demonstrates how newer generations of microcontrollers are integrating the analog and digital sides of design (so-called mixed-signal designs) into one chip, vastly simplifying the whole design process from initial design to hardware layout.

Microchip-mcu-family — A block diagram of Microchip’s newest MCU family, the PIC 24F GC, shows the internal functions available to designers, including two different types of memory and a range of analog functions such as ADCs, DACs, and operational amplifiers.

Size Matters
Also enabling designers to save valuable board space, Texas Instruments (TI) recently announced an expansion of tiny package sizes to several new families of the company’s ultra-low power MSP430 microcontrollers. Developers can now design smaller products with TI’s ultra-low power FRAM-based MSP430FR5738 and Flash-based MSP430F51x2 MCUs in wafer-level chip scale packages (WLCSP) as small as 2.0 x 2.2 x 0.3 mm, in addition to the five existing MSP430 MCU families with tiny package options. Devices with embedded FRAM memory provide longer battery lifetime because of the decreased power consumption.

The tiny package sizes make the MCUs well suited for a variety of ultra-low power applications such as sensor hubs, digital credit cards, ingestible sensors, health and fitness products like smart watches, and consumer electronics like tablets and notebooks.

The Right Tools for the Job
A large part of any successful design is having access to the right tools for the job. In designing microcontrollers for specific applications, probably the most important tool is good design software.

An example is TI’s expanded ecosystem of free and easy-to-use math libraries for its MSP430 microcontrollers. Both MSPMATHLIB and IQmathLib software libraries are well suited for applications where performance and power are critical, such as orientation tracking. For instance, it’s now possible to use an inverse tangent function to measure pitch and roll angles in a fraction of the time with an MSP430 MCU, an accelerometer and IQmathLib. Other applications include wireless sensor nodes, smart metering, heart rate monitors, and any product with capacitive touch or graphics capabilities.

TI-MSP430-microcontroller — A new family of TI’s MSP430 microcontrollers is available in wafer-level chip scale packages as small as 2.0 x 2.2 x 0.3mm. The small size and low power usage makes them ideal for a range of applications including medical products like ingestible sensors as well as commercial uses like digital credit cards.

MSPMATHLIB is an accelerated library of floating point, scalar math functions that complete math-intensive operations quickly. The advanced math library helps 16-bit MCUs execute code faster, which improves battery life in any math-intensive application.

IQmathLib helps developers optimize 16- and 32-bit fixed-point math. This math library provides the same benefits as MSPMATHLIB, but can achieve up to 100 times the performance, while only limiting the flexibility of the data range. IQmathLib provides all the back-end functions necessary to increase performance without sacrificing power consumption.

Making more resources available to designers such as large libraries of existing designs makes it much easier to use a reference design and tweak a few things to customize the design for the specific application. This saves a lot of engineering design time and resources and makes adding a microcontroller an attractive option.

For more traditional industrial motion control applications, for instance, TI’s InstaSPIN MOTION software works with the company’s C2000 family of microcontrollers. The software embeds the motion control algorithms needed to design a controller, allowing designers to focus on the specifics of the application.

The Internet of Things
Companies are also responding to the growing Internet of Things (IoT) phenomenon. For microcontrollers to work better with IoT applications, they have to have more and better communication options. Microcontroller manufacturer Atmel has come out with new families of microcontrollers to meet these needs. They offer, for instance, up to six configurable modules that can be configured as UART/USART, SPI, and I2C, along with a 12 Mbps USB 2.0 device with embedded host and device.

Microcontrollers 101

The first microcontrollers hit the market in the early 1970s. They were not much different from the then emerging microprocessors and required separate components for functions such as memory and communications.

There are a few basic types of microcontroller architectures. The Microchip PIC system, for instance, is based on a RISC architecture, which streamlines instruction processing and speeds up execution. Then there are the 8051-based systems, based on Intel’s x86 microprocessor family with a CISC architecture, which provides broader programming options but could also reduce execution speeds. Then there are microcontrollers from Atmel, specifically their AVR series, which are similar to PIC controllers but use a CISC architecture.

When evaluating microcontrollers, you should know a few key factors. Probably the first and most important is the size of the basic data unit. You’ll see microcontrollers referred to as 8-bit or 16-bit or 32-bit. This refers to the length of the data string, so an 8-bit MCU carries less information than a 16-bit MCU, which carries less than a 32-bit MCU, and so on. Other factors to consider are how much memory the MCU has and what is needed for the particular application, as well as any peripheral devices and if the MCU has these built in. For instance, if your MCU design involves motor control, a built-in PWM module may be needed. Other features may include support for specific communication protocols such as USB.

A fundamental difference between microcontrollers and microprocessors is probably the cost factor. That is, microcontrollers are generally less expensive than microprocessors. However, a microcontroller is designed for a limited, specific task, whereas a microprocessor is much more of a general purpose processor and also requires external memory and peripheral support. Of course, the nature of the application will determine the best fit.

Lastly are design tools, including libraries of functions of complex math and specific algorithms and reference designs. Perhaps the most important factor in the widespread adaptation of MCUs in so many applications is the ease with which they can be programmed and designed into systems. And for that, what’s needed are good support tools such as reference designs and libraries, as well as evaluation boards which allow designers to “breadboard” projects and test and debug them before committing to large production runs.

The Wide World of Microcontroller Acronyms

Techies love their acronyms, so it’s no surprise that the field is filled with acronyms and jargon. The microcontroller world has its share of specialized language and acronyms and here’s a partial list of some of the most common:

MCU – microcontroller (also μ C)
MIPS – million instructions per second; a measure of a processor’s speed and power
CPU – central processing unit; the basic instruction processing unit in a microprocessor/microcontroller
DSP – digital signal processor; another kind of chip designed for data intensive mathematical calculations, and less so for control applications
RISC – reduced instruction set computing
CISC – complex instruction set computing
SOC – system on a chip; a single integrated circuit (IC) that incorporates all elements of a computer on a single chip
ADC – analog-to-digital converter
DAC – digital-to-analog converter
RAM – random access memory
FRAM – ferroelectric RAM
UART – universal asynchronous receiver/transmitter; translates between parallel and serial data
SPI – serial peripheral interface; a synchronous serial data bus
PWM – pulse width modulation; a modulation technique used mostly for controlling electric motors